Phytoplankton size structure and water column metabolic balance in a coastal upwelling system: the Ría de Vigo, NW Iberia

Climate-induced variability of phytoplankton size structure influences primary productivity, marine food web dynamics, biosedimentation and exchange of CO2 between the atmosphere and ocean. Investigation of phytoplankton size structure in the Arctic Ocean is important due to rapid changes in its ecosystems related to increasing temperature and declining sea ice cover. We estimated the contribution of surface micro-, nano- and picophytoplankton to the total carbon biomass, chlorophyll a concentration and primary production in the Kara and Laptev Seas and investigated the relationships of these phytoplankton size groups with environmental factors which determine their spatial variability. Additionally, we compared chlorophyll specific carbon fixation rate, specific growth rate and carbon to chlorophyll ratios among different phytoplankton size groups. The investigation was carried out from August to September 2018. Generally, picophytoplankton was dominant in terms of chlorophyll a and primary production in the whole study area. The spatial variability of phytoplankton size classes was influenced by river discharge and relied mainly on water temperature, salinity and dissolved silicon concentration. Microphytoplankton prevailed across the river runoff region under conditions of low salinity and relatively high water temperature, while picophytoplankton was predominant under conditions of high salinity and low water temperature. Our study is the first to characterize size-fractionated phytoplankton abundance in the Kara and Laptev Seas, and provides a baseline for future assessment of the response of Kara and Laptev Sea ecosystems to climate-induced processes using phytoplankton size structure.

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Diatoms as a paleoproductivity proxy in the NW Iberian coastal upwelling system (NE Atlantic)

Biogeosciences ◽

10.5194/bg-14-1165-2017 ◽

2017 ◽

Vol 14 (5) ◽

pp. 1165-1179 ◽

Cited By ~ 8

Author(s):

Diana Zúñiga ◽

Celia Santos ◽

María Froján ◽

Emilia Salgueiro ◽

Marta M. Rufino ◽

...

Keyword(s):

Water Column ◽

Surface Sediment ◽

Sediment Trap ◽

Coastal Upwelling ◽

Late Summer ◽

Early Summer ◽

Marine Diatom ◽

Photic Zone ◽

Upwelling System ◽

Water Column Stratification

Abstract. The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 (±5.6) 106 valves m−2 d−1) represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom-derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Furthermore, Chaetoceros spp. dominate during spring–early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes.

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Changes in the characteristics of organic matter associated with hydrodynamics and phytoplankton size structure in the central-eastern Yellow Sea

The Science of The Total Environment ◽

10.1016/j.scitotenv.2021.151781 ◽

2021 ◽

pp. 151781

Author(s):

Yeonjung Lee ◽

Dong Han Choi ◽

Howon Lee ◽

Myung Jin Hyun ◽

Giyeong Kim ◽

...

Keyword(s):

Organic Matter ◽

Yellow Sea ◽

Size Structure ◽

Phytoplankton Size ◽

Central Eastern ◽

Phytoplankton Size Structure

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Spatial and temporal variability in coccolithophore abundance and distribution in the NW Iberian coastal upwelling system

Biogeosciences ◽

10.5194/bg-15-245-2018 ◽

2018 ◽

Vol 15 (1) ◽

pp. 245-262 ◽

Cited By ~ 10

Author(s):

Blanca Ausín ◽

Diana Zúñiga ◽

Jose A. Flores ◽

Catarina Cavaleiro ◽

María Froján ◽

...

Keyword(s):

Water Column ◽

Environmental Conditions ◽

Temporal Variability ◽

Coastal Upwelling ◽

Spatial And Temporal Variability ◽

Upwelling System ◽

Subsurface Waters ◽

Shelf Station ◽

Abundance And Distribution ◽

Upwelling Event

Abstract. A systematic investigation of the spatial and temporal variability in coccolithophore abundance and distribution through the water column of the NW Iberian coastal upwelling system was performed. From July 2011 to June 2012, monthly sampling at various water depths was conducted at two parallel stations located at 42∘ N. Total coccosphere abundance was higher at the outer-shelf station, where warmer, nutrient-depleted waters favoured coccolithophore rather than phytoplanktonic diatom blooms, which are known to dominate the inner-shelf location. In seasonal terms, higher coccosphere and coccolith abundances were registered at both stations during upwelling seasons, coinciding with high irradiance levels. This was typically in conjunction with stratified, nutrient-poor conditions (i.e. relaxing upwelling conditions). However, it also occurred during some upwelling events of colder, nutrient-rich subsurface waters onto the continental shelf. Minimum abundances were generally found during downwelling periods, with unexpectedly high coccolith abundance registered in subsurface waters at the inner-shelf station. This finding can only be explained if strong storms during these downwelling periods favoured resuspension processes, thus remobilizing deposited coccoliths from surface sediments, and hence hampering the identification of autochthonous coccolithophore community structure. At both locations, the major coccolithophore assemblages were dominated by Emiliania huxleyi, small Gephyrocapsa group, Gephyrocapsa oceanica, Florisphaera profunda, Syracosphaera spp., Coronosphaera mediterranea, and Calcidiscus leptoporus. Ecological preferences of the different taxa were assessed by exploring the relationships between environmental conditions and temporal and vertical variability in coccosphere abundance. These findings provide relevant information for the use of fossil coccolith assemblages in marine sediment records, in order to infer past environmental conditions, of particular importance for Paleoceanography. Both E. huxleyi and the small Gephyrocapsa group are proposed as proxies for the upwelling regime with a distinct affinity for different stages of the upwelling event: E. huxleyi was associated with warmer, nutrient-poor and more stable water column (i.e. upwelling relaxation stage) while the small Gephyrocapsa group was linked to colder waters and higher nutrient availability (i.e. early stages of the upwelling event), similarly to G. oceanica. Conversely, F. profunda is suggested as a proxy for the downwelling regime and low-productivity conditions. The assemblage composed by Syracosphaera pulchra, Coronosphaera mediterranea, and Rhabdosphaera clavigera may be a useful indicator of the presence of subtropical waters conveyed northward by the Iberian Poleward Current. Finally, C. leptoporus is proposed as an indicator of warmer, saltier, and oligotrophic waters during the downwelling/winter regime.

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